Diphenols are monomeric starting materials for polycarbonates, polyiminocarbonates, polyarylates, polyurethanes, and the like. Commonly owned U.S. Pat. Nos. 5,099,060 and 5,198,507 disclose amino acid-derived diphenyl compounds, useful in the polymerization of polycarbonates and polyiminocarbonates. The resulting polymers are useful as degradable polymers in general and as tissue-compatible bioerodible materials for medical uses, in particular. The suitability of these polymers for their end use application is the result of their polymerization from diphenols derived from the naturally occurring amino acid, L-tyrosine. The disclosures of U.S. Pat. Nos. 5,099,060 and 5,198,507 are hereby incorporated by reference. These previously-known polymers are strong, water-insoluble materials that can best be used as structural implants.
The same monomeric L-tyrosine derived diphenols are also used in the synthesis of polyarylates as described in commonly owned U.S. Pat. No. 5,216,115 and in the synthesis of poly(alkylene oxide) block copolymers with the aforementioned polycarbonates and polyarylates, which is disclosed in commonly owned U.S. Pat. No. 5,658,995. The disclosures of U.S. Pat. Nos. 5,216,115 and 5,658,995 are also hereby incorporated by reference.
Commonly owned International Application No. WO 98/36013 discloses dihydroxy monomers prepared from α-, β- and hydroxy acids and derivatives of L-tyrosine that are also useful starting materials in the polymerization of polycarbonates, polyiminocarbonates, polyarylates, and the like. The preparation of polycarbonates, polyarylates and polyiminocarbonates from these monomers is also disclosed. The disclosure of International Application No. WO 98/36013 is also hereby incorporated by reference.
Synthetic, degradable polymers are currently being evaluated as medical implants in a wide range of applications, such as orthopedic bone fixation devices, drug delivery systems, cardiovascular implants, and scaffolds for the regeneration/engineering of tissue. Such polymers, when used as implants, are non-traceable without invasive procedures. A radio-opaque polymer would offer the unique advantage of being traceable via routine X-ray imaging. The fate of such an implant through various stages of its utility could be followed without requiring invasive surgery.
Davy et al., J. Dentist., 10(3), 254–64 (1982), disclose brominated derivatives of poly(methyl methacrylate) that are radio-opaque. Copolymerization with non-brominated analogs was required to obtain the thermomechanical properties required for its desired use as a denture base. Only in a small range of certain percentage concentrations of the bromo-derivative does the material exhibit acceptable thermomechanical properties. In addition, there is no disclosure that the materials exhibiting acceptable properties remain biocompatible following the addition of bromine to the polymer structure. In contrast to the polymers disclosed in this application, the brominated poly(methyl methacrylates) do not degrade. However, because the bromine atoms are located on the aliphatic ester side chain, upon side chain ester cleavage, the polymer loses its radio-opacity.
Horak et al., Biomater., 8, 142–5 (1987), disclose the triiodobenzoic acid ester of poly(2-hydroxyethyl methacrylate) to be useful as a radio-opaque X-ray imaging marker compound. The iodine content was reported to affect the contrast, volume, mechanical properties and hydrophobicity of the polymer. A proper balance of properties, including radio-contrast and swellability, was achieved through optimization of the iodine content. Again, this material does not degrade through the main chain and loses radio-opacity upon side chain ester cleavage because the iodine atoms are located on the ester side chain.
Cabasso et al., J. Appl. Polym. Sci., 38, 1653–66 (1989), disclose the preparation of a radio-opaque miscible polymer coordination complex of poly(methyl methacrylate) and a uranium salt, uranyl nitrate. The polymer does not degrade through the main chain and the biocompatibility of the uranyl nitrate complex is not reported, nor has the long-term stability of the complex in vivo been established.
Cabasso et al., J. Appl. Polym. Sci., 41, 3025–42 (1990), discloses the preparation of radio-opaque coordination complexes of bismuth bromide and uranyl hexahydrate with polymers prepared from acrylated phosphoryl esters containing 1,3-dioxalane moieties derived from polyols such as glycerol, D-mannitol, D-sorbitol, pentaerythritol and dipentaerythritol. The phosphoryl group was selected to provide stronger coordinating sites for the bismuth and uranium salts and to impart adhesive properties toward hard tissues. Preliminary biocompatibility data indicated satisfactory performance, but the polymer does not degrade through the main chain and the long-term stability of the complex in vivo is not reported.
Jayakrishnan et al., J. Appl. Polym. Sci., 44, 743–8 (1992), discloses radio-opaque polymers of triiodophenyl methacrylate and of the iothalamic ester of 2-hydroxyethyl methacrylate. Polymers of useful molecular weight were not obtained, attributable to the presence of bulky iodine atoms in the monomer side chain. It was possible to obtain copolymers with non-iodinated analogs in the presence of crosslinking agents, such that up to 25% of the iodinated monomer could be incorporated. Preliminary biocompatibility data indicated that the presence of triiodophenyl methacrylate caused blood hemolysis. In addition, the materials also do not degrade through the main chain, and in the event of side chain ester cleavage, would lose their radio-opacity because of the iodine atoms being located in the side chain.
Kraft et al., Biomater., 18, 31–36 (1997), discloses the preparation of radio-opaque iodine-containing poly(methyl methacrylates). The monomers were ortho- and para-iodo and 2,3,5-triiodobenzoic acid esters of 2-hydroxymethyl methacrylate, and the para-iodophenyl ester of methyl methacrylic acid. The monomers were copolymerized with one or more non-iodinated analogs and a small amount of crosslinkers to produce polymer hydrogels with varying iodine contents. It was reported that the hydrogels were well tolerated by subcutaneous tissues and that the presence of iodine did not severely alter the swellability of the hydrogel. No tissue necrosis, abscess formation or acute inflammation was observed, although all implants were surrounded by a fibrous capsule. However, these materials also do not degrade through the main polymer chain, and upon side chain ester cleavage, lose radio-opacity because of the iodine atoms being located in the ester side chain.
Currently, no technology is available to provide radio-opaque polymers that degrade through the main polymer chain, such as the above-discussed tyrosine-derived polymers. For their intended use as medical implants, radio-opaqueness is a valuable property. A need exists for radio-opaque polymers that degrade through the main polymer chains, such as the tyrosine-derived polymers discussed above.